conf: do not steal pointers from the pool source

Since commit fcbbb289 we steal the pointer to the storage pool
source name if there was no pool name specified.

Properly duplicate the string to avoid freeing it twice.

https://bugzilla.redhat.com/show_bug.cgi?id=1436400
(cherry picked from commit e9f96909)

src/conf/storage_conf.c

@@ -845,8 +845,9 @@ virStoragePoolDefParseXML(xmlXPathContextPtr ctxt)
 
     ret->name = virXPathString("string(./name)", ctxt);
     if (ret->name == NULL &&
-        options->flags & VIR_STORAGE_POOL_SOURCE_NAME)
-        ret->name = ret->source.name;
+        options->flags & VIR_STORAGE_POOL_SOURCE_NAME &&
+        VIR_STRDUP(ret->name, ret->source.name) < 0)
+        goto error;
     if (ret->name == NULL) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
                        _("missing pool source name element"));

tests/storagepoolxml2xmlout/pool-logical-noname.xml

+<pool type='logical'>
+  <name>zily</name>
+  <uuid>1c13165a-d0f4-3aee-b447-30fb38789091</uuid>
+  <capacity unit='bytes'>0</capacity>
+  <allocation unit='bytes'>0</allocation>
+  <available unit='bytes'>0</available>
+  <source>
+    <name>zily</name>
+    <format type='lvm2'/>
+  </source>
+  <target>
+    <path>/dev/zily</path>
+    <permissions>
+      <mode>0700</mode>
+      <owner>0</owner>
+      <group>0</group>
+    </permissions>
+  </target>
+</pool>

tests/storagepoolxml2xmltest.c

@@ -79,6 +79,7 @@ mymain(void)
     DO_TEST("pool-logical");
     DO_TEST("pool-logical-nopath");
     DO_TEST("pool-logical-create");
+    DO_TEST("pool-logical-noname");
     DO_TEST("pool-disk");
     DO_TEST("pool-disk-device-nopartsep");
     DO_TEST("pool-iscsi");